Bone conduction audiphone



Ali@ 6 19416 H. KOCH BONE CONDUCTION AUDIPHONE Filed Dec. 5l, 1941 Il l.Il u n Lm. Mwr. h 2, .6 .A A \s 5 .1 .1 M 3 n 3 1 I' Plas,

, INVENTOR- f/f/VA'Y HOCH l I? Mm EY5 BYl Patented ug. 6, i946 BONECONDUCTION AUDIPHONE Henry Koch, Jamaica, N. Y., ass'gnor to DictographProducts Company, Inc., New York, N. Y., a corporation of Delaware 'inApplication December 31, 1941, serial No. 425,03919/ 8 Claims. 1

This invention relates to audiphones and has particular reference toaudiphone receivers having a vibrating contactor adapted to be placed inoperative connection with the bone 'structure of the user fortransmitting audible sounds picked up by a suitable microphone to theinner ear through the bone str'ucture.

Bone conduction receivers may be divided into two general classes,direct acting and reaction. In the former the bone contactor is directlyconnected to the vibrating element, such as a reed, of anelectromagnetic system, the magnet structure of which is held`relatively stationary by a headband or the like, so that the contactorvibrates relatively thereto. In the reaction type of receiver, the boneengaging contactor connected to the vibrating element, such as a reed,is supported by a headband or the like, so that the electromagneticsystem hangs free and, inasmuch as this system has substantial mass, itremains stationary while the contactor vibrates relatively thereto byreaction.

Each class of bone conduction receiver has certain advantages over theother, as well as certain disadvantages. action type of receivervibrates bodily as a unit, it necessarily also vibrates the connectingportion of the headband as well, which imposes some restraint on thevibration requiring increased Thus, inasmuch as the remass against whichthe reed may react, thus ren quiring considerable power for operation.

The direct acting bone receiver does not re- Uluire vibration of theheadband since only the reed and contactor are vibrated, but thenecessary pressure of the contactor against the bone in order to obtaingood conduction is considerable, and that results in suppression of thereed or diaphragm to which the contactor is connected and variation ofthe air gap. This objection to direct action receivers is largelyovercome in the improvement disclosed in my Patent No. 2,144,458, inwhich the contactor, forming part of the casing wall engaging the body,is carried by the reed, which is made suiiciently stiff to resistdeformation and consequent varying of the air gap under headband normalpressures.

Nevertheless, under abnormal conditions, a greater pressure is appliedto the button, sometimes on the order of a pound or more, so that thestiff reed cannot withstand this abnormal pressure and is eXed withconsequent variance of the air gap and ineicient and ineffectivereproduction. In one form of the invention of my said patent, resilientmaterial, such as rubber or felt is interposed between the contactor andthe casing carrying the magnetic structure 'so that even under abnormalpressures on the contactor the air gap is not varied suliiciently toimpair operation of the device. However, even though this cushion isresilient, it aiects normal electromagnetic vibration and is notentirely satisfactory.

The present invention is concerned With improvements on thedirect-acting bone receiver disclosed in my said Patent No. 2,144,458,in which the general characteristics of the receiver there disclosed areretained and the disadvantage of susceptibility to abnormal pressures cfthe contactor against the head is eliminated. This is accomplished in apreferred embodiment of the present invention by resiliently mountingthe entire magnetic structure in the casing by spring means softer orless resistant to flexing than the stiff reed, i. e., which will ieXbefore the reed fleXes under abnormal pressures, so that the entireelectromagnetic system ioats within the casing to be restored to itsnormal position by the spring means when the abnormal pressure isreleased, without impairment in its operation during the period ofabnormal pressure.

The receiver of this invention is also preferably mounted directly onthe headband which lies iiatvvise against the head so that any pressureagainst vthe headband will not change the position of theelectromagnetic structure resiliently supported within the casing in themanner described. y l

For a more complete understanding of the invention, reference may be hadto the accompanying drawing, in which:

Figure 1 illustrates the bone conduction receiver of this inventionsupported cn a headband and connected in a microphone circuit;

Fig. 2 is a longitudinal section through the receiver illustrating theinterior construction thereof; and

Fig. 3 is a longitudinal section through a modied form of the receiverof this invention.

Referring to Fig. l, the bone conduction receiver A includes a casing I0ofv hard rubber, phenolic resin, or the like, mounted on a headband Il,which forms a closure for the corresponding open side of the casing I0and also serves as a face plate for the receiver .A as it is heldflatwise against the head. Projecting slightly beyond the surface of theface plate Il is a bone-engaging contactor or button l2, which isvbrated by electrical means within the casing lil so as to transmit itsvibrations through the intervening bone to the inner ear of the user.The electrical means .3 is energized by voice currents picked up by asuitable microphone I3 ln circuit with a battery or other source ofpower I4 and preferably a vacuum tube or carbon booster amplifier, notshown, connected to the electrical means within the casing A by theflexible electric cord I5 having the separable plug type connectors I6plugged into the casing I0.

The aforemetioned electrical means within the casing Iil may beelectromagnetic, a piezo-electric crystal, or any other means responsiveto energization by voice currents to produce sufficiently powerfulvibrations for intelligible transmission through the bone to the innerear. Electromagnetic means are shown in the drawings by way ofillustration of the invention, and in Fig. 2 comiprises a bar magnet I'Iresiliently supported within the casing IB by means of a leaf spring I8secured at one end thereto by screws I9 and at its other end to the faceplate II', as by bolts 20 countersunk in the face plate I I YAlsosecured to the same end of the bar magnet I'I is the reed 2 I, having agenerally L shape and forming at its free end a narrow air gap 22 withthe opposed end of the pole shoe 23 secured to the other end of the barmagnet I1 by screws 24 and carrying the voice coil 25. The reed 2l andthe magnet I'I are free of and spaced from face plate I I' and casingI0, respectively.

Voice coil 425 is connected to connector plugs IB by filaments 26soldered to studs 2l on conductor plates 28 insulated from headband I Iand connected through springs 29 and friction buttons 30 to the plugsI6.

Secured to the free end of the reed 2I is a contactor button I2 whoseouter surface projects only slightly beyond the skin engaging surface offace plate I I'. For a small area contactor I2 as shown such slightprojection is desired in order that the skin beneath it will becompressed slightly more than the surrounding skin beneath the faceplate I I', so that the skin is firm and hence more conductive of thevibrations at the point of application thereof.

The average degree of skin compressibility, over the mastoid eminence,for example, is such that the projection of the contactor I2 beyond theface plate II need not exceed from l@ to 1&2 of` an inch, so that thebutton is substantially flush with the face plate. The degree ofprojection of the contactor in the drawings is shown exaggerated in theinterest of clarity. It will be understood that where the contactorconstitutes a large vpart or all of the area of the face plate, as shownin my aforementioned patent, there will be less or no projection of thecontactor beyond the faceplate, because the need for localized skincompression decreases as the area of the contactor increases.

The contactor I2 extends through a hole in the face plate II', which issuiciently oversize that there is no contact between the contactor I2and the face plate I I'. The consequent narrow annular slot around thecontactor I2 is sealed by a ring of felt 3| against ingress of moisture,dirt and the like, this ring 3I being clamped between the contactor I2and the reed 2 I The air gap 22 has a width on the order of a fewthousandths of an inch and the reed 2I 'is thick and consequently stiff,so that a force on the contactor I2 in excess of normal headbandpressures, i. e., greater than about five ounces, is necessary in orderto deflect the reed 2| suficiently to aifect the air gap 22. Thus, ifthe stiffness selected for reed 2l is such that a force of eight ouncesis lnecessary to deflect it at the air gap,

the stiffness of spring I8 is made such that it flexes before the reed2I is flexed, e. g., when a pressure in excess of six to seven ounces isapplied to the contactor I2. These degrees of stiffness are predicatedon normal headband pressures in the neighborhood of ve ounces, so that apressure in excess thereof is abnormal. Obviously, if the normalheadband pressure is greater or less than that in the given example, thereed 2| will be made stiffer or softer, as the case may be, and springI8 will always be made to flex under a contactor pressure somewhat lessthan that required to deflect the reed 2 I.

In operation of the bone conduction receiver il iustrated in Figs. 1 and2, the face plate I I' is held firmly against the head, such as on themastoid eminence, by the headband II, with a normal pressure of fiveounces. The contactor I2 does not move under this pressure because thestiffness of the reed 2I is such that a greater'pressure is required onthe contactor I2 before the reed is flexed. Consequently the contactorcompresses the skin beneath it slightly more than does the surroundingskin-engaging portion of the face plate I I', so that a rm vibrationconducting coupling between it and the bone is provided. Energization ofthe electromagnetic system results in vibration of the contactor I2relatively to the headband II and casing I and transmission of itsvibrations through the intervening bone to the inner ear.

If the pressure on the contactor I2 is increased abnormally, as when theuser presses on the casing I0 while it is on his head, or presses hisfinger on the contactor I2 while the receiver is not on his head, thespring I8 will ex, allowing the contactor I2 to recede into the casing,the entire magnet system moving therewith without any flexing of thereed 2l. Even when the device is in use and the casing is pressedagainst the head or a tight hat placed over the headband II producing asimilar effect, the operation of the receiver is not impaired.

By securing the lcasing Ill to the headband II, as shown, so that alarge area of the latter engages the head, the effect of pressure on theheadband, as by a tight hat, is minimized and usually precluded. Thisadvantage is not possible with headbands of the pivoted fork type Shownin my said patent, where the headband is spaced fromthe head and henceis more susceptible of movement and consequent suppression of thecontactor under abnormal pressures. It will be understood that thisarrangement of headband co-extensive with or continuous with the faceplate may be employed with advantage on any type of bone receiver, suchas those described in my said patent.

In the modied form of the invention shown in Fig. 3, the bar magnet II'is suspended by a spring i8' from the inside of the casing I0 to whichspring I8 is secured by bolts 32 located opposite the center of themagnet II. Secured to opposite ends of magnet I'I' by screws 33 is aU-shaped spring 34 carrying at its center the armature 35 screwed tocontactor I2', which may be a hard rubber button or other non-metallicmaterial. Pole shoes 23' also secured to the ends of the bar magnet I'Iby the screws 33 form narrow air gaps with the armature 35 and carry thevoice coils 25' connected in the microphone circuit through filaments26', bushings 36, and connectors I6'.

The contactor projects slightly beyond the surface of the face plate II,which is coextensive face plate l l.

with vthe 'headband Il, and a felt washer 3| seals the annular spacebetween the perimeter ofthe contactor l2 and the hole therefor in the Asbefore, th'e spring 34, which corresponds tothe reed 2l of Fig. '1 as aspring, is suicientlystilf that it does not lleX under pressures ofbutton i2 on the bone equal to normal or slightly greater, dependingupon requirements. However, spring I8 is softer than spring 34, so thatit ilexes under abnormal pressures on contactor I2', allowing the entireelectromagnetic structure to move inwardly until equilibrium isobtained. When the pressure is released the system is restored by springI8', without impairment of the operation of the re-v ceiver during thisinterval of abnormal pressure. The arrangement of Fig. 3 differs fromthat of Fig. 2 in that the ux paths are shorter and the movement underabnormal pressure is in the direction of the pressure instead of aboutspring i8 as a form of pivot in Fig. 2. The operation is the same ineach case.

It will be seen that the present invention provides a simple andeffective solution to the problem of operation of bone conductionreceivers, while preserving th'e advantages thereof, and while certainpreferred embodiments of the invention have been illustrated anddescribed herein, it is to be understood that they are merelyillustrative and do not limit the invention within the scope of theclaims.

I claim:

l. In an audiphone receiver, the combination of an electromagnetic meansadapted to respond to varying currents substantially throughout theaudible frequency range, a casing having a face plate adapted to engagethe body of the user, a contactor forming at least part of thebodyengaging surface of said face plate and vibrated by saidelectromagnetic means relatively to said casing, relatively stif springmeans connectingr said contactor and electromagnetic means, andresilient means connecting said electromagnetic means directly connectedto said casing and supporting said electromagnetic means, spring meansand contactor for bodily movement of the same as a unit relatively tosaid face plate in response to excessive pressures applied to saidcontactor, said resilient means having a stiffness less than that ofsaid spring means.

2. In an audiphone receiver, the combination of an electrical meansadapted to respond to varying currents substantially throughout theaudible frequency range, a casing having a face plate adapted to engagethe body of the user, a contactor forming at least part of thebody-engaging surface of said face plate and vibrated by said electricalmeans relatively to said casing, relatively stiff spring meansconnecting said contactor and electrical means, means supporting saidface plate and contactor in simultaneous connection with the bonestructure of the user with a predetermined pressure less than thatrequired to substantially flex said spring means, and resilient meansdirectly connecting said electrical means to said casing and supportingsaid electrical means, spring means and contactor and said supportingmeans for bodily movement of the same as a unit relatively to said faceplate under pressure on said contactor greater than said predeterminedpressure.

3. In an audiphone receiver, the combination of an electrical meansadapted to respond to varying currents substantially throughout theaudible frequency range, a casing enclosing said electrical means, aheadband secured to said casing and forming ak wall thereof vengagingthe body of the user with a predetermined pressure, resilient meansdirectly connecting said electrical means to said casing for bodilymovement re1- atively thereto, said resilient means having a stiffness.precluding substantial flexing under pressures approximately equal tosaid predetermined pressure, a contactor vibrated by said electricalmeans and extending through said wall for engaging the body of the usersimultaneously with said wall, and spring means connecting saidcontactor to said electrical means and having a stiffness greater thanthat of said resilient means, whereby pressure on said contactor inexcess of said predetermined pressure causes flexing of said resilientmeans and bodily movement of said electrical means, spring means andoontactor as a unit relatively to said casing.

4. In an audiphone receiver, the combination of an electrical meansadapted to respond to varying currents substantially throughout theaudible frequency range, a headband having a relatively flat portionadapted to engage the head of the user, a casing for said electricalmeans having a wall coextensive with said headband portion, and acontactor vibrated by said electrical means and adapted to engage thehead of the user simultaneously with said headband portion.

5. In an audiphone receiver, the combination of an electrical meansadapted to respond to varying currents substantially throughout theaudible frequency range, a headband having a relatively flat portionadapted to engage the head of the user, a contactor vibrated by saidelectrical means and substantially flush with said headband portion fortransmitting its vibrations through the bone to the inner ear, and acasing for said electrical means mounted on said headband.

6. In an audiphone receiver, the combination of electro-magnetic meansadapted to respond to varying currents substantially throughout theaudible frequency range, said electromagnetic means comprising a unitincluding a magnet structure, voice coil, vibratory armature, arelatively stilf spring connecting said armature and magnet structureand a contactor connected to said armature for vibration therewith, acasing for said electromagnetic means, said contactor forming at leastpart of a wall of said casing, resilient means directly connecting saidmagnet structure to said casing and having less stiffness than saidspring, whereby excessive pressure on said contactor causes saidresilient means to flex to permit bodily movement of saidelectromagnetic means as a unit relatively to said casing.

7. In an audiphone receiver, the combination of electromagnetic meansadapted to respond to Varying currents substantially throughout theaudible frequency range, said electromagnetic means comprising a unitincluding a magnet structure, voice coil, vibratory armature, arelatively stiff spring connecting said armature and magnet structureand a contactor connected to said armature for vibration therewith, aheadband having an aperture for said contactor, a casing for saidelectromagnetic means mounted on said headband, said headband forming awall of the casing, and resilient means directly connecting said magnetstructure to said Casing and having a stilfness less than said spring,whereby band having an aperture for said contacter, a casing for saidelectromagnetic means mounted von said headband, said headband forming awall of the casing, and a second spring directly connecting said magnetstructure to said headband and affording bodily movement of saidelectromagnetic means as a unit relatively to said casing in a directionopposite to that of application of the contacter to the body of theuser, said second atively sti spring connecting said armature and 1ospring having less stiffness than Said first Spring.

magnet structure and a contacter connected to said armature forvibration therewith, a head- HENRY KOCH.

